Methods for treating odors

ABSTRACT

There are provided methods for treating a gas having an undesirable odor. The methods comprise contacting the gas with an acidic aqueous oxidizing composition having a pH of about 2.0 to about 3.0 and comprising at least one cation of a metal; a sequestering agent; and H2O2 and submitting the gas and the composition to UV radiation when the gas and the composition are contacting each other, wherein the treatment permits to reduce by at least 60% intensity of the undesirable odor.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. Ser. No.16/264,778, filed on Feb. 1, 2019, that is a continuation application ofU.S. Ser. No. 15/347,332, filed on Nov. 9, 2016 that is a continuationapplication of U.S. Ser. No. 14/836,757, filed on Aug. 26, 2015, that isa divisional application of U.S. Ser. No. 12/989,155 filed on Dec. 20,2010, that is a 35 USC 371 national stage entry of PCT/CA2009/000641filed on May 8, 2009, and which claims priority from U.S. provisionalapplication 61/051,716, filed on May 9, 2008. These documents are herebyincorporated by reference in their entirety.

TECHNICAL FIELD

The present document relates to the field of odor treatment. Moreparticularly it relates to methods for treating odors. For example,odors present in a fluid can be treated by using such methods.

BACKGROUND OF THE DISCLOSURE

Industrial activity has always generated odors in the ambient air whichwere and are still able to worry the neighborhood. Despite theimplementation of tighter environmental regulations, this problemremains present even more so since, in certain locations, new commercialand residential sectors are developed in proximity to these sources.

The use of biofilters for reducing the odors has demonstrated itseffectiveness. However, their installation requires large surface areasthat are not always found on the industrial sites. The odorous gasemitters must then make do with technologies that are more compact andwhich have limitations due to the nature of the chemical compounds.

Each of the chemical compounds has different characteristics with regardto its solubility in water or another solvent, its olfactory thresholdand its partial pressure which ensure that the technologies currentlyused are limited whether this is as regards the effectiveness of thetreatment or else the lifetime of the materials used.

For such situations where a problem of space and of the use of compacttechnologies reaches limits, it would be highly desirable to be providedwith an alternative technology.

SUMMARY OF THE DISCLOSURE

According to one aspect, there is provided a method for method fortreating a fluid having an undesirable odor, the method comprising:

-   -   contacting the fluid with a basic aqueous oxidizing composition        comprising at least one cation of a metal chosen from Fe, Cu,        Ni, Mn, Ti, Cr, Ce, Zn, Pd, Mo, and mixtures thereof and H₂O₂;        and    -   contacting the fluid with an acidic aqueous oxidizing        composition comprising at least one cation of a metal chosen        from Fe, Cu, Ni, Mn, Ti, Cr, Ce, Zn, Pd, Mo, and mixtures        thereof and H₂O₂,

The fluid can be contacted with the basic aqueous oxidizing composition,and then the fluid can be contacted with the acidic aqueous oxidizingcomposition, or the fluid can be contacted with the acidic aqueousoxidizing composition, and then the fluid can be contacted with thebasic aqueous oxidizing composition. The method can optionally furthercomprise contacting the fluid with activated carbon.

According to another aspect, there is provided a method for treating afluid having an undesirable odor, the method comprising:

-   -   contacting the fluid with a basic aqueous oxidizing composition        comprising at least one cation of a metal chosen from Fe, Cu,        Ni, Mn, Ti, Cr, Ce, Zn, Pd, Mo, and mixtures thereof and H₂O₂;        and/or contacting the fluid with an acidic aqueous oxidizing        composition comprising at least one cation of a metal chosen        from Fe, Cu, Ni, Mn, Ti, Cr, Ce, Zn, Pd, Mo, and mixtures        thereof and H₂O₂; and    -   contacting the fluid with activated carbon.

The fluid can be contacted with the basic aqueous oxidizing composition,and then the fluid can be contacted with the acidic aqueous oxidizingcomposition, or the fluid can be contacted with the acidic aqueousoxidizing composition, and then the fluid can be contacted with thebasicaqueous oxidizing composition.

According to another aspect, there is provided a method for treating afluid having an undesirable odor, the method comprising:

-   -   contacting the fluid with an acidic aqueous oxidizing        composition comprising at least one cation of a metal chosen        from Fe, Cu, Ni, Mn, Ti, Cr, Ce, Zn, Pd, Mo, and mixtures        thereof and H₂O₂    -   submitting the fluid and the composition to an UV radiation.

The fluid can optionally be further contacted with a basic aqueousoxidizing composition and/or with activated carbon.

It was found that such methods are very effective for treatingundesirable and/or unpleasant odors. Such technologies can be operatedat low costs and represent a simple manner to treat fluids.

In the methods previously described, the fluid can comprise at least oneorganic compound chosen from carboxylic acids, thiols, thioethers,disulfides, alcohols, aldehydes, amines, amides and mixtures thereof.The carboxylic acids can comprise C₁-C₂₀ carboxylic acids. The thiolscan comprise C₁-C₂₀ thiols. The thioethers can comprise C₂-C₂₀thioethers. The disulfides can comprise C₂-C₂₀ disulfides. The alcoholscan comprise C₁-C₂₀ alcohols. The aldehydes can comprise C₁-C₂₀aldehydes. The amines can comprise C₁-C₂₀ amines. The amides cancomprise C₁-C₂₀ amides.

In the methods previously described, the fluid can be passed through abed of activated carbon. Such a treatment can be carried out before orafter a treatment with a basic or acidic oxidizing composition.

The fluid can be treated with the basic aqueous oxidizing compositionand then with the acidic aqueous oxidizing composition. Alternatively,the fluid can be treated with the acidic aqueous oxidizing compositionand then with the basic aqueous oxidizing composition.

The fluid can be treated with the basic aqueous oxidizing composition soas to at least partially oxidize at least one compound responsible forthe undesirable odor and then the fluid can be treated with the acidicaqueous oxidizing composition so as to at least partially oxidize atleast one compound responsible for the undesirable odor, thereby atleast partially reducing intensity of the undesirable odor.

The fluid can be treated with the acidic aqueous oxidizing compositionso as to at least partially oxidize at least one compound responsiblefor the undesirable odor and then the fluid is treated with the basicaqueous oxidizing composition so as to at least partially oxidize atleast one compound responsible for the undesirable odor, thereby atleast partially reducing intensity of the undesirable odor.

The methods can further comprise submitting the fluid and the acidicaqueous oxidizing composition to UV radiation, when the fluid and theacidic aqueous oxidizing composition are contacting each other. Themethod can also further comprise submitting the fluid and the basicaqueous oxidizing composition to UV radiation, when the fluid and thebasic aqueous oxidizing composition are contacting each other.

For example, the fluid can be contacted with the acidic aqueousoxidizing composition so as to at least partially dissolve at least onecompound responsible for the undesirable odor and contained in the fluidinto the acidic aqueous oxidizing composition and wherein the method canfurther comprise submitting, the at least one compound that is at leastpartially dissolved into the acidic aqueous oxidizing composition, to UVradiation.

For example, the fluid can be contacted with the basic aqueous oxidizingcomposition so as to at least partially dissolve at least one compoundresponsible for the undesirable odor and contained in the fluid into thebasic aqueous oxidizing composition and wherein the method can furthercomprise submitting, the at least one compound that is at leastpartially dissolved into the basic aqueous oxidizing composition, to UVradiation.

The fluid can be contacted with the acidic aqueous oxidizing compositionso as to at least partially dissolve at least one compound responsiblefor the undesirable odor and contained in the fluid into the acidicaqueous oxidizing composition and the at least one compound that is atleast partially dissolved into the acidic aqueous oxidizing compositioncan be submitted to UV radiation so as to at least partially oxidize theat least one compound and at least partially reduce intensity of theundesirable odor.

The fluid can be treated with the basic aqueous oxidizing compositionand/or with the acidic aqueous oxidizing composition so as to at leastpartially oxidize at least one compound responsible for the undesirableodor and then the fluid can be passed through a bed of activated carbon,thereby at least partially reducing intensity of the undesirable odor.

In the methods previously described, the basic and/or acidic compositioncan comprise a cation of a metal chosen from Fe, Cu, Ni, Mn, Ti, Cr, Ce,Zn, Pd, Mo, and mixtures thereof. For example, the metal can be Fe, orCu. In another example, the composition can comprise a cation of Fe.

For example, the cations can be chosen from Fe²⁺, Cu²⁺, Ni²⁺, Mn²⁺,Ti⁴⁺, Cr³⁺, Ce³⁺, Zn²⁺, Pd²⁺, Mo⁶⁺, and mixtures thereof. According toanother example, the cation can be Fe²⁺, or Cu²⁺. According to anotherexample, the cation can be Fe²⁺.

The sequestering agent (or chelator), when oxidation occurs in a basicaqueous composition, can be chosen from diethylenetriaminepentaaceticacid (DTPA), nitrolotriacetic acid (NTA), ethylenediaminetetraaceticacid (EDTA), sodium hexametaphosphate, sodium citrate, and mixturesthereof. For example, the sequestering agent can be DTPA or NTA.Alternatively, the sequestering agent can be an ion exchange resin suchas zeolites. For example, the sequestering agent can be NTA and thecation can be Fe²⁺. The sequestering agent (or chelator), when oxidationoccurs in an acidic aqueous composition, can be chosen fromethylenediaminetetraacetic acid (EDTA), oxalic acid, citric acid,glycine, NTA, salicylic acid, sulfosalicylic acid, trithylenetetramine,and mixtures thereof. For example, the sequestering agent can be oxalicacid.

For example, the sequestering agent can be present at a concentration ofat least 30 mg/L, about 30 mg/L to about 480 mg/L or about 60 mg/L toabout 240 mg/L

In the previously described methods, contacting can include mixing thefluid with the basic oxidizing composition so as to at least partiallydissolve at least one compound contained in the fluid into the basicoxidizing composition. The fluid and the basic oxidizing composition canbe mixed together in a packed column. For example, the fluid can beintroduced at a bottom portion of the column and the basic aqueouscomposition can be introduced at a top portion of the column. The fluidand the basic aqueous composition can be mixed together into the columnover a predetermined amount of transfer units.

For example, the fluid, before contacting the basic aqueous oxidizingcomposition, can be at a temperature of about 10° C. to about 85° C.,about 25° C. to about 55° C., or about 15° C. to about 40° C.

For example, the metal cation can be present in the basic composition ata concentration of at least 1 mg/mL, at least 5 mg/mL, or at least 20mg/mL. about 1 mg/L to about 20 mg/L or about 2 mg/L to about 10 mg/L.

For example, the concentration of H₂O₂ in the basic composition can beat least 20 mg/L, about 20 mg/L to about 2000 mg/L, or about 50 mg/L toabout 700 mg/L.

The basic aqueous oxidizing composition can comprise a base chosen fromNaOH, KOH, Mg(OH)₂, Ca(OH)₂, NaHCO₃, Na₂CO₃, K₂CO₃, KHCO₃, and mixturesthereof. The basic composition can have a pH of at least 9.0. Forexample, the pH can be of about 9.3 to about 11.5, about 9.5 to about10.5, about 9.7 to about 10.0, or about 9.8.

In the previously described methods, contacting can include mixing thefluid with the acidic oxidizing composition so as to at least partiallydissolve at least one compound contained in the fluid into the acidicoxidizing composition. The fluid and the acidic oxidizing compositioncan be mixed together in a packed column. For example, the fluid can beintroduced at a bottom portion of the column and the acidic aqueouscomposition can be introduced at a top portion of the column. The fluidand the acidic aqueous composition can be mixed together into the columnover a predetermined amount of transfer units.

The acidic aqueous oxidizing composition can comprise an acid chosenfrom H₂SO₄, HCl, HNO₃, H₃PO₄, and mixtures thereof.

The acidic aqueous oxidizing composition can have a pH of at least 1.5,about 1.5 to about 4.0, about 2.0 to about 3.0, or about 2.2 to about2.6.

The metal cation can be present in the acidic aqueous oxidizingcomposition at a concentration of at least 5 mg/L, at least 10 mg/L, orat least 20 mg/L. The concentration can also be about 10 mg/L to about200 mg/L, about 20 mg/L to about 100 mg/L, about 50 to 150 mg/L, orabout 30 mg/L to about 50 mg/L. For example such a cation can be Fe²⁺,Cu²⁺ or a mixture thereof. For example, the concentration of H₂O₂ in theacidic composition can be at least 100 mg/L, about 100 mg/L to about3500 mg/L, or about 1000 mg/L to about 2500 mg/L.

For example, H₂O₂ can be present in the acidic aqueous oxidizingcomposition at a molar ratio H₂O₂:metal of at least 5:1, at least 10:1,or at least 20:1.

For example, H₂O₂ can be present in the acidic aqueous oxidizingcomposition at a molar ratio H₂O₂:metal of about 10:1 to about 100:1, or12:1 to 40:1.

For example, the fluid, before contacting the acidic aqueous oxidizingcomposition, can be at a temperature of about 10° C. to about 85° C. orabout 15° C. to about 40° C.

In the methods previously defined, the treatment can permit to reduce byat least 50%, by at least 60%, by at least 70%, by at least 75%, by atleast 80%, by at least 85%, by at least 90%, by at least 95%, by atleast 97%, by at least 98%, of about 50% to about 99%, of about 60% toabout 99%, of about 70% to about 97%, or of about 70% to about 99% theintensity of the at least one indesirable odor.

The expression “sequestering agent” as used herein includes chemicalmoieties that bind to, or complex with, any cation or anion. Examples ofsequestering agents or chelators are well known in the art. For example,the sequestering agent can bind to a metal cation.

The expression “packed column” as used herein refers to an absorptiontower, in which the packing is used so as to increase contact between agas and a liquid. For example, such a packed column can be used forremoving a contaminant from a gas stream by absorbing it or dissolvingit into a liquid (such as an oxidizing composition).

The term “fluid” as used herein refers to a gas, a liquid or a mixturethereof.

BRIEF DESCRIPTION OF DRAWINGS

The following drawings represent in a non-limitative manner, variousexamples:

FIG. 1 shows a bloc diagram of an example of a method for treating afluid;

FIG. 2 shows a bloc diagram of another example of a method for treatinga fluid; and

FIG. 3 shows a bloc diagram of a further example of a method fortreating a fluid.

DETAILED DESCRIPTION

Further features and advantages will become more readily apparent fromthe following non-limitative examples:

The following examples are non-limiting examples.

EXAMPLES

In order to determine the effectiveness of each of the treatments thatare part of the examples, dynamic olfactometry measurements have beencarried out. The olfactometer is composed of six beakers in which threetest specimens are found. Each beaker corresponds to a differentdilution level of the odorous gas. In each of these beakers, a singletest specimen diffuses odorous air. Each of the individuals that make upthe panel must identify, in each beaker, which of the test specimensdiffuses the odorous gas. If the individual does not detect any odors,the person passes to the next beaker. The data from the panel arecompiled and the results are calculated with the aid of a table by usingthe air dilution and odorous gas flow rates of each of the testspecimens.

Example 1: Treatment by Oxidation and Absorption in Consecutive Basicand Acidic Media

The gas to be treated contains several organic compounds which,depending on their nature, are more soluble in a basic medium or in anacidic medium. In the present examples, compounds such as butyric acid,valeric acid, sulfides and disulfides were found to be compounds thatare more soluble in a basic media and certain amines were found to bemore soluble in an acidic media. FIG. 1 is a bloc diagram concerning themethod carried out in Example 1.

The gas was treated by passing it through a packed column in which abasic aqueous oxidizing composition (comprising H₂O₂ and NaOH and havinga pH of about 10.0) was flowing. The oxidizing composition containedabout 510 mg/L of hydrogen peroxide, about 4 mg/L of Fe and NTA at aconcentration of four times higher than the concentration of Fe on amolar basis. The temperature of the medium was about 22° C. The gas flowrate was about 3000 m³/h. Fe can be provided in various form such asFeSO₄, FeCl₂ or any suitable source of Fe²⁺. A reactor was disposed atthe bottom of the column, and the oxidizing composition was recirculatedfrom the reactor to a top portion of the column by means of a pump. Thefluid was introduced at a bottom portion of the column in acounter-current manner.

Then, the gas is treated in a second packed column that also comprisesan oxidizing composition comprising hydrogen peroxide. The compositionflowing in the second column was an acidic aqueous oxidizing composition(H₂SO₄) having a pH of about 2.2. The oxidizing composition containedabout 2360 mg/L of hydrogen peroxide, and about 50 mg/L of Fe. Thetemperature of the medium was about 23° C. The gas flow rate was about3.6 m³/h.

These conditions were maintained for 19 days and five dynamicolfactometry analyses were carried out. The results were the following(average values):

-   -   odor level at the inlet: 131;    -   odor level after 1st treatment: 69;    -   effectiveness after 1st treatment: 47%;    -   odor level after 2nd treatment: 36; and    -   effectiveness after 2nd treatment: 73%.

Example 2: Treatment by Oxidation and Absorption in a Basic Medium andAdsorption onto Activated Carbon

In the present example, a gas similar to the one treated in example 1was treated by using a similar set-up. FIG. 2 is a bloc diagramconcerning the method carried out in Example 2.

The gas was treated by passing it through a packed column in which abasic aqueous oxidizing composition (comprising H₂O₂ and NaOH and havinga pH of about 9.8) was flowing. The oxidizing composition containedabout 75 mg/L of hydrogen peroxide, about 2 mg/L of Fe and NTA at aconcentration of four times higher than the concentration of Fe on amolar basis. The temperature of the medium was about 21° C. The gas flowrate was about 2040 m³/h.

Subsequently, the gas was treated by passing it through a bed ofactivated carbon. The temperature of the gas was about 24° C. at a gasflow rate of about 3 m³/h. The height of the activated carbon was about180 mm.

These operating conditions were maintained for 5 days and 8 olfactometrymeasurements were taken. The results are the following:

-   -   odor level at the inlet: 155;    -   odor level after 1st treatment: 70;    -   effectiveness after 1st treatment: 55%;    -   odor level after 2nd treatment: 5; and    -   effectiveness after 2nd treatment: 97%.

Example 3: Treatment by Oxidation and Absorption in a Basic Media andthen, in an Acidic Media in which Oxidation is Enhanced by UV Radiation

In the present example, a gas similar to the one in example 1 wastreated by using a similar set-up. FIG. 3 is a bloc diagram concerningthe method carried out in example 3.

The gas was treated by passing it through a packed column in which abasic aqueous oxidizing composition (comprising H₂O₂ and NaOH and havinga pH of about 9.8) was flowing. The oxidizing composition containedabout 300 mg/L of hydrogen peroxide, about 2 mg/L of Fe and NTA at aconcentration of four times higher than the concentration of Fe on amolar basis. The temperature of the medium was about 22° C. The gas wasat a temperature of about 50° C. and a flow of 80 L/min.

Then, the gas was treated in a second packed column that also containedan oxidizing composition comprising hydrogen peroxide. The compositionflowing in the second column was an acidic aqueous oxidizing composition(HNO₃) having a pH of about 2.4. The oxidizing composition containedabout 350 mg/L of hydrogen peroxide, about 30 mg/L of Fe and oxalic acidat was concentration of four times higher than the concentration of Feon a molar basis. The temperature of the medium was about 22° C. The gasflow was about 80 L/min.

As explained in example 1, the mixture of the gas and the compositionwas flowing down from the packed column to a reactor. In Example 3, themixture of the fluid and the composition in the reactor were submittedto UV radiation in order to enhance the oxidation rate of the organiccompounds that cause the unpleasant and/or undesirable odor. The UVradiation was produced by a 254 nm lamp at a power of 9 Watts. After apredetermined residence time in the reactor, the mixture is recirculatedto the top of the packed column to complete the loop.

These operating conditions were repeated over more than 30 tests. Eachtest was carried out over a period of time of about 8 to about 12 hours.The same amount of olfactometry measurements were taken. The resultswere the following:

-   -   odor level at the inlet: 386    -   odor level after 1^(st) treatment: 127    -   effectiveness after 1^(st) treatment: 66%    -   odor level after 2^(nd) treatment: 50    -   effectiveness after 2^(nd) treatment: 86%

It can thus be seen that the results presented in examples 1 to 3clearly show that these three different methods permit to considerablyreduce the intensity (or odor level) of the undesirable odor. It canthus be the that such methods permit to efficiently at least partiallyreduce the intensity or an undesirable or unpleasant odor.

The methods have been described with regard to specific examples. Thedescription as much as the drawings were intended to help theunderstanding of the document, rather than to limit its scope. It willbe apparent to one skilled in the art that various modifications may bemade to the methods previously defined without departing from the scopeof the document as described herein, and such modifications are intendedto be covered by the present document.

1-89. (canceled)
 90. A method for treating a gas having an undesirableodor, said method comprising: contacting said gas with a basic aqueousoxidizing composition having a pH of about 9.0 to about 10.0, andcomprising H₂O₂ at a concentration of about 20 mg/L to about 700 mg/Land a cation of a metal chosen from Fe, Cu, Ni, Mn, Ti, Cr, Ce, Zn, Pd,Mo, and mixtures thereof, wherein said contacting includes mixing saidgas with said basic oxidizing composition so as to at least partiallydissolve at least one compound contained in said gas into said basicoxidizing composition, said gas and said basic oxidizing compositionbeing mixed together in a packed column, and wherein said gas isintroduced at a bottom portion of said column and said basic aqueouscomposition is introduced at a top portion of said column, said gas andsaid basic aqueous composition being mixed together into said columnover a predetermined amount of transfer units and submitting said gasand said composition to UV radiation when said gas and said compositionare contacting each other, wherein said treatment permits to reduce byat least 70% intensity of said undesirable odor, as determined bydynamic olfactometry measurements carried out by a panel of individuals,in which the olfactometer was composed of six beakers in which threetest specimens were found, each beaker corresponded to a differentdilution level of the odorous gas and wherein in each beaker, a singletest specimen diffused odorous air, each of the individuals that made upthe panel had to identify, in each beaker, which of the test specimenswas diffusing the odorous gas, the data from the panel were compiled andthe results were calculated with the aid of a table by using the airdilution and odorous gas flow rates of each of the test specimens. 91.The method of claim 90, wherein said treatment permits to reduce by atleast 80% intensity of said undesirable odor, as determined by dynamicolfactometry measurements been carried out by a panel of individuals.92. The method of claim 90, wherein said treatment permits to reduce byat least 85% intensity of said undesirable odor, as determined bydynamic olfactometry measurements been carried out by a panel ofindividuals.
 93. The method of claim 90, wherein said basic aqueousoxidizing composition has a pH of about 9.3 to about 9.7.
 94. The methodof claim 90, wherein said basic aqueous oxidizing composition has a pHof about 9.0 to about 9.5.
 95. The method of claim 90, wherein saidbasic aqueous oxidizing composition has a pH of about 9.5 to about 10.0.96. The method of claim 90, wherein the at least one cation is Fe²⁺,Cu²⁺, or a mixture thereof.
 97. The method of claim 90, wherein the atleast one cation is Fe²⁺.
 99. The method of claim 90, wherein said basicaqueous oxidizing composition further comprises a sequestering agent.100. The method of claim 99, wherein said sequestering agent is chosenfrom diethylenetriaminepentaacetic acid (DTPA), nitrolotriacetic acid(NTA), ethylenediaminetetraacetic acid (EDTA), sodium hexametaphosphate,sodium citrate, and mixtures thereof.
 100. The method of claim 99,wherein said sequestering agent is NTA.
 101. The method of claim 99,wherein said sequestering agent is DPTA.
 102. The method of claim 1,wherein said method further comprises contacting said gas with an acidicaqueous oxidizing composition.
 103. The method of claim 102, wherein thegas is treated with the basic aqueous oxidizing composition and thenwith the acidic aqueous oxidizing composition.
 104. The method of claim102, wherein the gas is treated with the acidic aqueous oxidizingcomposition and then with the basic aqueous oxidizing composition. 105.The method of claim 102, wherein said gas is contacted with an acidicaqueous oxidizing composition having a pH of about 2.0 to about 3.0 andcomprising at least one cation of a metal chosen from Fe, Cu, Ni, Mn,Ti, Cr, Ce, Zn, Pd, Mo, and mixtures thereof; sequestering agent chosenfrom ethylenediaminetetraacetic acid (EDTA), oxalic acid, citric acid,glycine, NTA, salicylic acid, sulfosalicylic acid, trithylenetetramine,and mixtures thereof; and H₂O₂ wherein said contacting includes mixingsaid gas with said acidic oxidizing composition so as to at leastpartially dissolve at least one compound contained in said gas into saidacidic oxidizing composition, said gas and said acidic oxidizingcomposition being mixed together in a packed column, and wherein saidgas is introduced at a bottom portion of said column and said acidicaqueous composition is introduced at a top portion of said column, saidgas and said acidic aqueous composition being mixed together into saidcolumn over a predetermined amount of transfer units; and submittingsaid gas and said composition to UV radiation when said gas and saidcomposition are contacting each other.
 106. The method of claim 105,wherein the acidic aqueous oxidizing composition comprises Fe²⁺, Cu²⁺,or a mixture thereof.
 107. The method of claim 105, wherein the acidicaqueous oxidizing composition comprises Fe²⁺.
 108. The method of claim105, wherein said acidic aqueous oxidizing composition has a pH of about2.2 to about 2.6.
 109. The method of claim 105, wherein saidsequestering agent is oxalic acid.